Blade ring for radial flow elastic fluid turbines and method for producing same



June 27, 1933. A, LYSHOLM ET AL 1,916,175

BLADE RING FOR RADIAL FLOW ELASTIC FLUID TURBINES AND METHOD FOR PRODUCING SAME Filed Nov 20, 1929 2 Sheets-Sheet l June 27, 1933. A. LYSHOLM ET AL 1,916,175

B E RING FOR RADIAL FLOW ELAST FLUID BINES AND METHOD FOR PRQDUC SAME Filed Nov. 20, 1929 2 Sheets-Sheet 2 ["3 5 i f 5 7 f! 78 W//%\\\ M 7/W/Ai 11 O ,5 4 42 V A WM 7/ ?4 1 2! I I? dK M 75 A T f4 25 7' PM", 1 13114 3 im@ 19 i. i Z 27 42' l W A W Patented June 27, 1933 UNITED STATES: PATENT- OFFICE.

ALF LYSHOLM, OF STOCKHOLM, AND GUSTAV KARL WILLIAM. BOESTAD, OF LIDINGO,

SWEDEN, ASSIGNORS TO AKTIEBOLAGET LJUNGSTROMS ANGTURBIN, OF STOCK- HOLM, SWEDEN, A JOINT STOCK COMPANY OF SWEDEN BLADE RING FOR RADIAL FLOW ELASTIC FLUID TURBINES AND METHOD FOR PRODUCING SAME Application filed November 20, 1929, Serial This application is a continuing application in part with respect to application Serial No. 374,227 filed June 27,1929 and, as to common subject matter, relates back to said application Serial No. 374,227 for all dates and rights incident to the filing thereof and the filing of foreign applications correspondin g thereto.

The present invention relates to elastic fluid turbines and has particular reference to the blade ring structure of radial flow turbines of the type comprising a plurality of radially spaced, axially telescoped blade rings, each of which blade rings comprises axially spaced annular rings, hereinafter to be referred to as ring bonds, and a plurality of blades situated between and connected'at' their ends to the ring bonds. 7

In accordance with known practice,'turbineblades in blade rings of the above character may be connected to the ring bonds in numerous different ways. Thus, blade lengths of proper profile may have their ends inserted in suitable apertures in relatively light annular fastening rings and these rings together with the blade ends may be secured to the ring bonds by welding, riveting or other mechanical operations. Again, each blade may be made separately with integral blade roois at its ends and the blade roots secured directly to the ring bonds by mechanical connections of any suitable character, such for example as dovetails, slots, grooves, threaded projections and the like; Permancnt fixing or locking of such connections may also include rolling or pressing operations on the me? al or one or more of the parts to impart to such parts a permanent deformation operating to hold the parts in gripped relation.

The forces to which blade rings are subjected during normal turbine operation, particularly centrifugal force, produce bending moments tending to flex or'deflect the parts.

particularly the blades, and the produced stresses are of such magnitude that it has heretofore been considered necessary, in view of the character of known methods of blade attachment, to consider the-blades as beams freely supported at their ends when cal- No. 4085591 and in Sweden July 6, 1928.

as to produce in the blade ring structure initial bending moments or stresses tending to counteract the bending moments to which the parts of the blade ring are subjected due to rotation of the parts. By this practice we are enabled to so reduce the effect of the stresses produced during normal operation that the blades may be calculated as beams fixed at their ends. mensions of the blades for a given turbine may be made less than if the prior art practice were followed, .with resulting economies in space, weight and cost.

As will'hereinafter be pointed out more fully, the proposed method is applicable to a wide variety of structural arrangements and is also susceptible to variation in the Consequently the diparticular manner of its application. A.

characteristic feature of the method is the production of initial stresses in the finished blade ring tending to deflect the blades. These stresses may be set up due to deforma-' tion or deflection of the portion of the blade ring comprising the ring bonds or the portion of the blade. ring comprising the blades, or both, and such deformation or deflection may be caused prior to, during or after thestep of joining the blades to the ring bonds.

For a better understanding of the invention, both as to the method employed and the means for carrying the method into effect, reference may be had to the accompanying drawings forming a part of this specification, which drawings illnstrate various forms of apparatus embodying the invention, and the ensuing description thereof.

In the drawings:

Fig. 1 is a section of a part of radial flow elastic fluid turbine of the type to which the invention is particularly applicable;

Figs. 2 to 8 inclusive are axial sections on an enlarged scale of blade ring structure embodying the principles of the invention, these figures illustrating various steps in the manufacture of the blade rings and some of the figures illustrating in exaggerated manner the deflections of the parts with which the present invention is concerned;

Figs. 9 to 12 inclusive illustrate the application of the invention to blade ring structure employing a different kind of joint between the blades and the ring bonds, Figs. 9, 11 and 12 being axial sections similar to Figs. 2 to 8 and Fig. 10 being a transverse section of a portion of a blade ring; and

Figs. 13 to 15 are sections similar to Figs. 2 to 8 illustrating still another form of blade ring construction.

Referring to Fig. 1, the broken line 1 indicates the center line or axis of rotation of the turbine shaft 2 of a radial flow turbine, the broken line 3 indicating a radial plane with respect to which the turbine is axially symmetrical. The turbine illustrated comprises four blade systems designated at 4, 5, 6 and 7. Steam is admitted through the inlet passage 8 and passes serially through the blade systems in the order named. In the radial'flow blade systems 4, 5 and 6, alternate blade rings, considered in the direction of steam flow, are supported by the turbine rotor indicated generally at 14, the remaining blade rings being supported by a similar turbine disc or rotor (not shown) Rotation of adjacent blade rings in opposite direction is caused by flow of steam through the blade' systems. In Fig. 2 there is shown in section and on a larger scale a blade ring comprising two axially spaced annular ring bonds 11 and 12 between which are located a series of axially parallel peripherally spaced turbine blades 10, one only of which is shown in the section. The ring bond 12 is connected by means of an annular expansion ring 13 to a part of the turbine rotor 14, this construction being well known in the art.

Each of the blades 10in the blade ring is provided at its ends with projections 15 and 16. The projections 15 of each blade abut against the projections of adjacent blade, so that the projections 15 of a complete set of blades form a projecting annular ring;

Likewise, the projections 16 of a complete set of blades form a projecting annular ring. These projecting rings are threaded as indicated in the figure. Ring bonds 11 and 12 are provided, respectively, with annular grooves 15a and 16a, these grooves being threaded so as to receive the threaded pro-' jections15 and 16 on the ends of the blades.

The above described type of threaded connection between blades and ring bonds may advantageously be made in accordance with the method disclosed in the copending application of Gosta L. B. Wahlsten, Serial No. 374.226 filed June 27, 1929. In accordance with this method, the blades are held in their proper position relative to each other, and prior to the machining of the ends of the blades, by placing them on a suitable mandrel and casting low fusion point metal around the blades so that the blades and the cast metal form an annular cylinder, the ends of which may be readily turned so as to form the proper threaded projections 15 and 16 on the blade ends. The ring bonds are then, in accordance with this method, screwed on to the blade ends and after the blade ring is assembled, the low fusion point metal is melted from between the blades. \Vhile this method is convenient in the manufacture of blades having threaded end connections, it is not essential to the present invention either with respect to blades having threaded connections or blades having different types of connections.

If a blade of the form shown in Fig. 2 is assembled without the imposition of any initial stresses in the material, that is, if the projections 15 and 16 and grooves 15a and 16a are respectively in alignment prior to assembly, with the parts in unstressed condition, the blades and ring bonds will be deflected during normal operation of the turbine in the manner indicated in exaggerated form in Fig. 3. During normal operation the blades, supported only at their ends, are subjected to centrifugal forces acting radially outwardly, which forces produce bending moments tending to deflect the blades and ring bonds in the manner shown in Fig. 3.

If. however, the blade ring is made by a process which subjects the blade ring structure to initial stress tending to flex or defleet, the blades radially inwardly by the application thereto of bending moments caused by the initial stress, the blade ring, when the turbine is not in operation, will assume the shape indicated in exaggerated form in Fig. 4. IVhen a blade ring of the type illustrated in Fig. 4 is subjected to the radially outwardly acting centrifugal forces caused by normal operation of the turbine, the blade ring structure will be deflected from the position shown in Fig. 4 to the position shown in exaggerated manner in Fig. 5. As will be evident from a comparison of Figs. 3 and 5 the blades in the latter figure may be considered as beams fixed at their ends. For a given set of operating conditions, other factors being equal, the unit stresses in elements of this character will be less than the unit stresses in blades which must be considered as beams freely supported at their ends. Consequently, for given conditions, blades in a ring having initial stress of the character shown in Fig. 4 are subjected to lower unit stresses than the blades in a similar ring constructed in the manner shown in Fig. 2. If it is not required to reduce the unit stress in the blades below the value which would obtain in a ring obtained. In accordance with the practicedisclosed in this figure, the blades are made axially straight. The ring bonds, however, are made so that in their initial unstressed condition,-they are tapered axially. Before the ring bonds are secured to the blades, they are deflected to a cylindrical form by any suitable mechanical means. Such means may comprise any form ot'appariztus such as a clamping member or mandrel indicated 'diagramniatically at 18 in Fig. 8, upon which the rings may be forced or shrunk. \Vhen the rings are deflected to cylindrical form, they are placed under an initial stress tending to return them to their original tapered shape. With the ring bonds under this initial stress,

the threaded projections 15 and 16 of the blades are screwed into the corresponding grooves 1n the ring bonds and after assembly of the blade ring is completed, the clamping members are removed from the ring bonds and the tendency of the ring bonds to return from the full line position indicated at the left of Fig. 8 to the dotted line position shown (which position correspondsto the original position of the bonds as shown in Fig. 6) tends to flex the blades to the position shown in Fig. 4:.

In accordance with the above practice, the flexing force applied to the blades is due solely to the tendency of the ring bonds to re turn to their original unstressed shape. This force may be augmented by a bending force ormoment tending to bend the blades, which is produced by forming the parts of the ring bonds and blades which contact when these elements are connected so that they tend, when assembled, to produce bending stresses on the blades independently of the initial stress of the ring bonds.

In the form of blade ring illustrated in Fig. 6, this may be accomplished by making the outer annular projections li of the ring bonds higher than the inner annular projections 17a. With this construction, it will be evident that when the parts are screwed together, the projections 17 will abut against the ends of the blades, before the projections 17a and will consequently tend to deflect the centers of the blades radially inwardly when the parts are screwed together until both the projections 17 and 17a are seated against the ends of the blades.

In the illustrated arrangement, the deflection of-the blade rings is caused by the combined action of the projections of uneven height on the blade rings and the initial flexing of the ring bonds. It will be evident that blade rings can be made in which the flexing of the blades is secured by either one of these factors alone.

It may be desirable to reduce the value of the stresses in the ringbonds which are imposed thereon during normal operation of the turbine. In this event, the ring bonds are advantageously made tapering as at 11a in Fig. 7, the direction of the taper, however, being opposite the direction of taper shown in Fig. 6. Ring bonds made in this manner when deflected to cylindrical form, assembled to the blades, and then released tend to bend the blades initially to a position such as'indicated in Fig. 3, which position is more or less the same as that to which centrifugal forces tend to flex the blades. For this reason the effect of the centrifugalv forces in tending to twist the. ring bonds is reduced or eliminated since centrifugal forces merely act in this instance to assist the-ring'bonds in bending the blades to a position resulting in the return of the ring bonds to their unstressed shape. If it is desired to make use of the additional initial stress which can be produced by the use of uneven projections, the projection 17c on the ring bond 11a may he made of lesser height than the projection 17d.

In'Figs. 9 to 12, the application of the invention to blade rings having a different type of joint is illustrated. -In this form of blade ring the blades 10 are provided with blade roots 20 and 21 adapted to fit in radially extending grooves 22 and 23 in the ring bonds 11 and 12 respectively. These grooves may be radially tapered as shown in Fig. 12. In order to make use of the invention in connectlon with rings of this character. the ring bonds 11 and 12 are advantageously made of tapering form and then deflected by force into cylindrical form through the medium of suitable clamping or mandrel members indicated diagrammatically in Fig. 11 at 18. With the ring bonds held to cylindrical form so that initial stress is produced therein. the blade roots are inserted in the corresponding grooves in the ring bonds and upon release of the latter from the holding means, the tendency of the ring bonds to assume their original positions as shown at 11 and 12 in Fig. 9 will produce bending moments tending to bend the blades to the shape shown in Fig. 4-.

Figs. 13 to 15 illustrate the application of the invention to still another form of blade ring construction in which the blades are provided with blade roots 24 and 25 at their ends, the blade roots being dovetailed as illustrated. Tapered ring bonds 11 and 12 of the type heretofore described are employed,

these blade rings bein provided with annular grooves 26 and 2 adapted respectively ISO to receive the blade roots 24 and 25. The ring bonds are deflected to cylindrical form as indicated in Fig. 14. The dovetailed b'ade roots are inserted in the grooves 26 and 27 and are then permanently fixed in the grooves by suitable rolling or pressing operations acting to force the metal at the edges of grooves 26 and 27 into the recesses of the dovetails. This deformation of the metal in the ring bonds is indicated diagrammatically as being accomplished by the roller 28. The finished construction is indicated at the right of Fig. 15 and, as in the previous constructions, the tendency of the ring bonds to return to their original form, upon their release from the holding means, produces the desired bending moments acting on the blades.

From the foregoing description, it will be evident that the present invention is not limited to any particular form of connection between blades and ring bonds but may be applied to many different forms. It is also evident that the particular manner of producing the initial stresses in the ring bonds need not be that herein shown by way of example. Other equivalent ways may be employed as for instance by making the ring bonds initially of cylindrical form and deflecting them to a conical form to produce the initial stresses, so that the desired bending moments will be produced after release of the ring bonds from the holding means, due to the tendency of the ring bonds to return to their original cylindrical form.

While we. have, in accordance with the patent statutes, described examples of the best practice known to us, it is to be understood that the invention is not limited to the specific method and means hercinabove described by way of illustration, but is to be considered as embracing all such methods and means as may fall within the scope of the appended claims. It is. further to be understood that within the scope of the invention certain of the features disclosed herein may be utilized to the exclusion of others and that various features disclosed may becombined within the scope of the invention in various different:-

ways.

lVhat we claim is 1. The method of making blade rings of the type comprising axially spaced ring bonds having contact surfaces and blades between the ring bonds having cooperating contact surfaces adapted to abut against said first named contact surfaces in rigidly secured relationship which consists in providing blade rings and blades with cooperating contact surfaces disposed so that the cooperating surfaces cannot be brought into abutting relation in a completely assembled blade ring without deflection of one or more of the parts of the blade ring, and assembling the parts to form a complete blade ring with the coto their undefiected state.

rncy of the ring bonds to return operating surfaces in abutting relation while applying force to one or more of the parts to deflect the same.

2. That improvement in the method of making blade rings of the type comprising axially spaced ring bonds and blades therebetween which consists in deflecting said ring bonds from their normal state and holding them in their deflected state, rigidly securing the ends of the blades to the ring bonds while holding the ring bonds in deflected state and subsequently releasing the ring bonds whereby to cause the ring bonds to mpose a bending stress on the blades due to the tendency of the ring bonds to return That improvement in the method of making blade rings of the type comprising axially spaced ring bonds having blades therebetween and screwed thereto which consists in subjecting the ring bonds to stress sufficient to hold them in deflected state, screwing the ends of'the blades to the ring bonds while the latter are in said deflected state and then releasing the ring bonds from said stress whereby to produce stress on the blades due to the tendency of the ring bonds to return to their undeflected state.

4. The method of making blade rings of the type having grooved ring bonds and blades rigidly secured at their ends in said grooves which consists in deflecting the ring bonds from their normal unstressed state, insert-ing the ends of the blades in the grooves in the ring bonds with the ring bonds held in deflected state, locking the blade ends in the grooves by deforming the walls of the grooves with the ring bonds held in deflected state and subsequently releasing the ring bonds whereby to produce bending stresses tending to displace the central portions of the blades radially with respect to unstressed position due to the tendency of thcring bonds to return to their undeflected state.

5. Themethod of making blade rings of the type having axially spaced ring bonds and blades rigidly secured at their ends between the ring bonds which consists in deflecting the ring bonds from their normal unstressed state, forming a plurality of radially extending grooves in the ring bonds with the ring bonds held in deflected state, forming blades with end portions adapted to seat in said grooves, inserting said end portions in said grooves with the ring bonds held in deflected state and subsequently releasing the ring bonds whereby to produce Lending stresses tending to displace the centralportions of the blades radially with respect to unstressed position due to the tendto their undeflected state.

6. The method of making blade rings of the type having axially spaced ring bonds and blades rigidly secured at their ends to the ring bonds by dovetail connections which consists in deflectingthe ring bonds from their normal unstressed'state, forming pe ripheral grooves in the ring bonds with the ring bonds held in deflected state, forming dovetail projections on the ends of the blades, inserting the dovetail projections in the peripheral grooves with the ring bonds held in deflected state, locking the dovetail projections in the grooves by deforming the side walls in the grooves to foree them into contact with the sides of said dovetail projections with the ring bonds held in deflected state and subsequently releasing the ring bonds whereby to produce bending stresses tending todisplace the central portions of the blades radially with respect to unstressed position due to the tendency of the ring bonds to return to their-undeflected state.

7. A blade ring for radial flow elastic fluid turbines comprising a plurality of blades rigidly connected at their ends to spaced annular supporting members, said blades being subjected to bending moments transmitted thereto from each of said supporting members through the rigid connections, said bending moments tending to displace the central portions of the blades radially with respect to the end portions thereof.

8. A blade ring for radial flow elastic fluid turbines comprising a plurality of blades rigidly-connected at their ends to spaced annula r supporting members, said blades being subjected to bending moments transmitted .thereto from each of said supporting members through the rigid connections, said bending moments tending to displace the central portions of the blades radially inwardly with respect to the end portions thereof.

9. A blade ring for radial flow elastic fluid turbines comprising a plurality of blades rigidly connected at their ends to spaced annular supporting members, said blades being subjected to bending moments transmitted thereto from each of said supporting members through the rigid .connections, said bending moments tending to displace the central portions of the blades radially outwardly with respect to the end portions thereof. 10. A blade ring for radial flow elastic fluid turbines having a supporting portion comprising axially spaced ring bonds, and a blade portion comprising a plurality of blades between said ring bonds, said portions having means for rigidly connecting the portions, said means comprising circumferentially extending grooves on one portion and cooperating projections on the other portion,

said grooves and projectionsbeing formedso as to produce stresses acting and reacting between said portions when the projections are in assembled position in the grooves and tending to displace the central portions of the blades radially with respect to unstressed I position.

11. A blade ring for radial flow elastic fluid turbines having a supporting portion comprising axially spaced'ring bonds, and a blade portion com rising a plurality of blades between sai ring bonds, said portions having means for rigidly connecting the portions, said means comprising circumferentially extending threaded grooves on one portion and cooperating threaded projeetions on the other portion, said grooves and projections being formed so as to produce stresses acting and reacting between said portions when the projections arethreaded into the grooves, and tending to displace the central portions of the blades radially with respect to unstressed position.

12. A blade ring for radial flow elastic fluid turbines having a supporting portion comprising axially spaced ring bonds, and a blade portion comprising a plurality of blades between said ring bonds, said portions having means for rigidly connecting said portions, said means comprising grooves on one portion and cooperatlng projections on the other portion, said grooves and projections being formed so as to produce stresses acting and reacting between said portions when the projections are'in assembled position in the grooves, said stresses comprising bending moments tending to deflect the central portions of the blades radially with respect to the end portions'thereof.

13. A blade ring for elastic fluid turbines comprising axially spaced ring bonds, and blades between said ring bonds, said ring bonds and vblades having means for rigidly connecting the ends ofthe blades to the ring bonds comprising circumferential grooves in the axially confronting faces of the ring bonds and cooperating projections on the ends of the blades, said grooves and pro]ections being formed so as to produce stresses acting and reacting between the ring bonds and the blades when the projections are in assembled positionin the grooves and tending to displace the central portions of the blades radially with respect to unstressed position.

14. A blade ring for radial flow elastic fluid turbines having a supporting portlon comprising axially spaced ring bonds, and a blade portion comprising a plurality of blades between said ring bonds, said portlons having means for rigidly connect ng the portions, said meanscomprising circumferentially extending grooves on one portion and' application of stress to the other portion due to such deflection.

15. A blade ring for radial flow elastic fluid turbines having a supporting portion comprising axially spaced ring bonds, and a blade portion comprising a plurality of blades between said ring bonds, said portions having means for rigidly connecting the portions, said means. comprising circumferentlally extending threaded grooves on one portion and cooperating threaded projections bonds having contact surfaces and blades between the ring bonds having cooperating contact surfaces adapted to abut against said first named contact surfaces in rigidly secured relationship which consists in provlding ring bonds and blades with cooperating contact surfaces disposed so that the cooperating surfaces cannot be brought into abutting relation in a completely assembled blade ring without deflection of one or more of the parts of the blade ring, applying force to deflect one or more of the parts of the blade ring before assembling the parts and assembling the parts with said one or more parts in deflected state to form a complete blade ring with the cooperating surfaces in abutting relation.

In testimony whereof we afiix our signatures.

ALF LYSHOLM.

GUSTAV KARL WILLIAM BOESTAD. 

